Herefore, one of the frequently used means for measuring deposition in general, not necessarily crystal growth, involved the use of a so called quartz crystal monitor which was mounted adjacent the sample so that material was deposited on the quartz crystal simultaneously with the sample. The change in electrical frequency of the quartz crystal indicated how much material had been deposited. This technique for measuring deposition of crystal growth was difficult to use because what is deposited on the quartz crystal is not necessarily indicative of the crystal growth rate on the sample or substrate, particularly because the substrate was hot and the quartz crystal monitor was cold.
Another prior art technique for monitoring crystalline growth involved the use of electron diffraction to generate a diffraction pattern on a phosphor screen. In the diffraction-type type process an electron beam was directed to impinge on the sample at a very shallow angle and then opposite the electron gun on the other side of the sample a phosphor screen was mounted, whereby the electrons hit the sample at a very shallow angle and diffracted through the top layers of the crystal to produce a diffraction pattern on the screen. The present invention is an improvement over such prior art techniques.